Collection well for body fluid tester

ABSTRACT

A body fluid is collected for testing for an analyte contained within the body fluid. The fluid is collected in an apparatus including a reservoir for receiving and collecting a flow of body fluid from a discharge end of a conduit. A capillary test space is in fluid flow communication with the reservoir. The capillary test space is positioned to be in contact with the fluid in the reservoir after the fluid has accumulated to a predetermined transfer volume of fluid. The capillary test space is sized to wick the fluid from the reservoir when the fluid contacts the capillary test space.

TECHNICAL FIELD

[0001] This invention pertains to testing a body fluid for an analyte.For example, the present invention is applicable for testing glucose ina body fluid such as blood or interstitial fluid.

BACKGROUND

[0002] Numerous patents teach various ways for collecting a sample ofbody fluid and testing such fluid for an analyte such as glucose. Forexample, U.S. Pat. Nos. 5,823,973 and 5,820,570 describe methods andapparatus for obtaining, in one embodiment, interstitial fluid, which istested for glucose through IR absorption. These patents also describeuse of the disclosed inventions in colormetric and electro-chemicaltesting of glucose. U.S. Pat. No. 5,453,360 teaches a test strip forcolormetric testing for glucose. Blood is placed on a test stripcontaining various chemical components including a dye. The degree ofcolor change of the test strip indicates the amount of glucose. U.S.Pat. Nos. 5,508,171 and 5,628,890 teach electro-chemical testing. Bloodis placed on a test strip containing electrodes. Reaction of glucose onthe electrodes generates a current indicating the amount of glucosepresent in the blood.

[0003] Present development efforts are directed to testing very smallvolumes of body fluid (e.g. about 0.5 microliter). The use of such smallvolumes of fluid permits less painful collection of a fluid samples.However, small fluid volumes present additional challenges for analytetesting. For example, testing for analytes typically requires a fluidsample in excess of a predetermined minimum volume. By way ofnon-limiting representative example, a test may require a minimum samplesize of 5 microliter to yield reliable test results.

[0004] Furthermore, sample collection systems may receive a flow of bodyfluid over an extended time (e.g., 10 seconds or more) before a minimumsample volume is collected. As a result, body fluid may be deposited ontest components (e.g. electrodes or colormetric test strips) before afull sample is collected. Such premature deposit may initiate chemicalreactions on a test strip thereby consuming reagents before a reliabletest can be initiated. Further, such test components may be coupled tologic circuits for calculating an analyte's concentration based onreadings from the test strip. A premature deposit of an inadequatevolume of fluid sample may falsely inform logic circuits that testinghas initiated when, in fact, an adequate sample volume has yet to becollected.

[0005] Recognizing the problems of premature test initiation, the priorart has developed techniques for delaying test initiation until anadequate volume of sample is collected. For example, logic circuits mayhave a built-in time delay which assumes a fixed period of time tocollect an adequate volume of sample. Of course, such systems sufferfrom the fact there is no certainty that an adequate volume is collectedduring such time delay. Alternatively, to be conservative, such timedelays may frequently be unnecessarily long. Additionally, U.S. Pat. No.5,049,487 teaches reading a reflectance of a side of a membrane. A fluidsample is placed on the opposite side. When the sample is absorbedthrough the membrane, the change in reflectance is noted indicatingtesting may commence. However, such a system suffers from chemicalagents on the membrane being in contact with a sample prior toinitiating testing.

[0006] Therefore, there is a need for a method and apparatus forcollecting a sample of body fluid to obtain an adequate volume of suchfluid.

SUMMARY

[0007] According to a preferred embodiment of the present invention, amethod and apparatus are disclose for collecting a body fluid fortesting for an analyte contained within the body fluid. The apparatusincludes a reservoir for receiving and collecting a flow of body fluidfrom a discharge end of a conduit. A capillary test space is in fluidflow communication with the reservoir. The capillary test space ispositioned to be in contact with the fluid in the reservoir after thefluid has accumulated to a predetermined transfer volume of fluid. Thecapillary test space is sized to wick the fluid from the reservoir whenthe fluid contacts the entrance end. With the present invention, fluidis collected within the reservoir at a rate of flow limited by theconduit. When the reservoir is full, the collected fluid rapidly wicksinto the capillary test space. The capillary test space may contain testcomponents for testing for the analyte.

BRIEF DESCRIPTION OF THE DRAWINGS

[0008]FIG. 1 is a perspective view of a sample collection apparatus withan electrochemical test strip shown removed;

[0009]FIG. 2 is an enlarged segmented view of the area of circle 2 inFIG. 1;

[0010]FIG. 3 is a side-sectional view of the apparatus of FIG. 1 showingthe test strip in place;

[0011]FIG. 4 is an enlarged segmented view of the area of circle 4 inFIG. 3;

[0012]FIG. 5 is a segmented top-plan view of a reservoir of theapparatus of FIG. 1;

[0013]FIG. 6 is a view taken along line 6-6.in FIG. 3 and showing abolus of body fluid residing in a capillary test space;

[0014]FIG. 7 is a top plan view of a first alternative embodiment of thepresent invention;

[0015]FIG. 8 is a view taken along line 8-8 of FIG. 7;

[0016]FIG. 9 is a view similar to FIG. 8 showing a second alternativeembodiment of the present invention;

[0017]FIG. 10 is a view similar to those of FIGS. 8 and 9 showing athird alternative embodiment of the present invention;

[0018]FIG. 11 is a top plan view of the embodiment of FIG. 10 with atest strip removed; and

[0019]FIG. 12 is a view similar to FIG. 11 showing a fourth alternativeembodiment of the present invention

DETAILED DESCRIPTION

[0020] With reference to the various drawing figures in which identicalelements are numbered identically throughout, a description of apreferred embodiment will now be provided. Throughout this description,the present invention will be described with reference to collecting asample of interstitial fluid for glucose testing using a narrow needlethat penetrates into but not through the dermis as more fully describedin commonly assigned U.S. Pat. Nos. 5,823,973 and 5,820,570, thedisclosures for both of which are hereby incorporated herein byreference. While such a use is a preferred embodiment, the presentinvention is applicable to other fluid collection systems (e.g. bloodcollection) as well as testing for other fluid analytes. Further, thepresent invention is described with reference to using electro-chemicaltesting of a collected sample. The teachings of the present inventionare equally applicable to other testing methods such as colormetrictesting and IR absorption testing.

[0021] Referring now to FIGS. 1-6, a collection apparatus 10 includes amain body 12 and a test strip 14. The main body has a handle 16 and aneedle-containing ferrule 18. The ferrule 18 holds a hollow needle 20extending from a penetration end 22 to a discharge end 24. Thepenetration end 22 protrudes from a radially spaced ring end 26 of theferrule 18.

[0022] In a preferred embodiment, the penetration end 22 is axiallyspaced from ring end 26 by a distance sufficient for the needle 20 topenetrate into but not through a patient's dermis to collect a sample ofsubstantially blood-free interstitial fluid as taught in U.S. Pat. No.5,820,570. In such an embodiment, the outer diameter of the needle isabout 0.013 inch.(about 0.33 mm). This sizing of the needle permitssubstantially pain-free penetration of the needle to collect a bodyfluid. This description illustrates a preferred embodiment. Needle 20may be sized to collect any body fluid such as blood or interstitialfluid. Further, the present invention is disclosed where the skinpenetration member (i.e., the needle 20) also serves as a conduit forsupplying fluid to a reservoir 30 as will be described. The presentinvention is also applicable to any conduit for transporting a bodyfluid (e.g., a capillary tube as described in International ApplicationPCT/US97/08400 published Nov. 20, 1997 as International Publication No.WO 97/42883).

[0023] The test strip 14 contains exposed test components on an innersurface 14 a. The test components are shown in the form of electrodes 32for testing a body fluid for an analyte such as glucose throughelectrochemical testing. As previously described, the test componentscould be components. For alternate testing techniques such ascolormetric or IR absorption testing.

[0024] Not shown is a housing for holding the apparatus 10 during samplecollection and testing. Housings for holding disposable body fluidsamplers are shown in U.S. Pat. No. 5,823,973. Such housings may containelectrical components for electrical connection to the test stripelectrodes 32 to connect a signal from the electrodes 32 to logiccircuits to compute and report on the analyte in response to signalsfrom the electrodes 32 during testing.

[0025] The material of the main body 12 defines a cylindrical reservoir30 having a cylindrical axis between a first end 34 and a second end 36.In the embodiment shown, the axis of the reservoir 30 is perpendicularto the axis of the needle 20. Such a relative alignment is not necessaryfor adequate function and any other alignment is acceptable.

[0026] The reservoir 30 has a volume at least as great as a desired testvolume of body fluid to be tested. In a preferred embodiment, reservoir30 has a volume of 0.7 microliters. As will become apparent, fluid iscollected in the reservoir 30 and accumulates with a fluid level risingfrom the first end 34 toward the second end 36. Due to such smallvolumes and the geometry of reservoir 30, surface tension assures thefluid is retained in the reservoir 30 with the fluid level rising asdescribed regardless of the orientation of the apparatus 10 (i.e., theoperation of the apparatus 10 is gravity independent).

[0027] The discharge end 24 of the needle 20 is disposed within thereservoir 30 adjacent the first end 34. Accordingly, body fluid istransported from the penetration end 22, through needle 20 anddischarged from the discharge end 24 into the reservoir 30 at the firstend 34.

[0028] The material of the body 12 also defines an enlarged empty volume38 positioned between the reservoir 30 and the ferrule 18 andsurrounding the needle 20. The enlarged volume 38 is separated from thereservoir 30 by material of the main body pinching against the needle 20as at locations 40. The enlarged volume 38 has a volume larger than thereservoir 30 and ensures that fluid within the reservoir 30 is retainedwithin reservoir 30 as it accumulates. For example, in the absence ofenlarged volume 38, manufacturing tolerances may result in a narrowspacing between the material of main body 12 and needle 20. Such anarrow spacing could function as a capillary space communicating withreservoir 30 which would wick fluid out of reservoir 30. The enlargedvolume 38 precludes such capillary wicking. Further, the materialdefining the volume 38 is preferably hydrophobic to minimize wicking. Inthe event precise manufacturing permits complete liquid-tight sealingaround needle 20, the enlarged volume 38 could be eliminated.

[0029] The test strip 14 is secured to the main body (e.g., throughadhesives) with the inner surface 14 a facing the main body 12 andoverlying the second end 36 of the reservoir 30. The main body 12includes a groove 42 shaped complementary to the outer periphery of thetest strip 14 to ensure accurate alignment of the test strip 14 with themain body 12. Adjacent its outer periphery, the inner surface 14 a ofthe test strip 14 includes spacers 44 (shown best in FIG. 6). Thespacers 44 insure uniform and close parallel spacing of the innersurface 14 a from a test strip opposing surface 12 a of the main body 12for reasons that will become apparent. Alternatively, spacers could beformed on the body 12 thereby eliminating the need for spacers 44.

[0030] The test strip opposing surface 12 a includes a step 46. Withreference to FIG. 6, the construction described above results information of a capillary test space 48 defined between opposing surfacesof the test strip inner surface 14 a and step 46.

[0031] As shown in FIG. 6, the spacers 44 are spaced from opposingsurfaces of the step 46 thereby defining enlarged volumes 50 on oppositesides of the step 46. The enlarged volumes 50 perform a function similarto that of enlarged volume 38. Namely, if the spacers 44 were sized toabut step 46, small capillary spaces could form between the spacers 44and step 46. Such capillary spaces could wick fluid from the fluidreceiving volume 48. Again, if manufacturing could ensure a fluid-tightseal between spacers 44 and step 46, the volumes 50 could be eliminated.

[0032] Shown best in FIGS. 4 and 6, the electrodes 32 are positionedopposing the step 46. Further, the spacing S (FIG. 4) between the step46 and inner surface 14 a is uniform and is selected to be sufficientlynarrow for the capillary test space 48 to act as a capillary space towick fluid from the reservoir 30. An entrance end 52 of the capillarytest space 48 is positioned at the second end 36 of the reservoir 30(FIG. 4). The preferred spacing S is about 0.003-0.005 inch (about 0.075mm to 0.125 mm). The spacing S may be as large as 0.012 inch (about0.300 mm) or larger depending on the surface tension and volume of thefluid being collected and the relative hydrophobic/hydrophiliccharacteristics of the main body 12 and test strip 14.

[0033] A hole 54 is formed through the body 12 and into the fluidreceiving volume 48 on a side of the step 46 opposite the reservoir 30.The hole 54 permits air in the capillary test space 48 to be vented toatmosphere as fluid flows into the capillary test space 48 from thereservoir 30. Volumes 50 also provide venting.

[0034] An additional advantage of this embodiment is its ability tominimize the effects of sample concentration via evaporation. The totalair volume contained within the enclosed sections substantially definedby volume 38, reservoir 30, the capillary test space 48, and adjoiningvolumes spaces, is sufficiently small so as to provide a very lowcapacity for evaporation of water from the aqueous sample beingcollected. In addition, the location of the vent and the overallgeometry discourage convective passage of air through the aforementionedspaces, minimizing any convective acceleration of evaporation. Whendealing with small volumes (e.g. less than 1 microliter), minimizingevaporative losses can be important to maintaining the integrity of thesample for quantitative analysis.

[0035] With the construction thus described, the apparatus 10 is used byurging the ring end 26 against a patient's skin. The penetration tip 22penetrates the skin. The ring end 26 (being radially spaced from tip 22)acts to urge fluid into the needle 20. The fluid flows along the needle20 and discharges into the first end 34 of the reservoir 30 throughdischarge end 24. In one possible embodiment, suction could be appliedto advance the rate of flow of fluid through needle 20. Suction is notused in other embodiments.

[0036] Fluid accumulates in the reservoir 30 with a level of accumulatedfluid growing from the first end 34 to the second end 36. When the fluidlevel reaches the second end 36, a desired volume of fluid to be testedhas accumulated in the reservoir 30. At this time, the fluid levelcontacts the entrance end 52 of the capillary test space 48. Since thecapillary test space 48 is a narrow capillary space, the fluid israpidly wicked out of the reservoir 30 and into the capillary test space48 as a bolus delivery of fluid indicated by the bolus of fluid 56 inFIG. 6. So positioned, the fluid is in contact with the electrodes 32and testing of the fluid may commence.

[0037] The present invention permits fluid contact with the electrodes32 only after an adequate volume of fluid has been collected. By way ofnon-limiting representative example, it may take thirty seconds forfluid to fill the reservoir 30 and only one second for the accumulatedfluid to be wicked into the capillary test space 48 from the reservoir30. As a result, the present invention avoids a long-period of timeduring which fluid is contacting the electrodes 32 and before testingmay commence. Further, without the need for specialized electronics asused in the prior art, testing cannot commence until after an adequatevolume of fluid has been accumulated. Therefore, when a signal isreceived from electrodes 32, it is known that an adequate volume offluid is opposing the electrodes 32.

[0038] The retention of fluid in the reservoir 30 and wicking of fluidinto the capillary test space 48 can be controlled and modified byvarying the dimensions of the components as will be apparent to one ofordinary skill in the art having the benefit of the teachings of thepresent invention. Further, as will be apparent to such artisan, suchretention and wicking may also be controlled and modified throughmaterial selection. For example, it is desirable that the main body 12be formed of hydrophobic material and that the capillary test space 48be more hydrophilic. For example, a hydrophilic surfactant may beapplied to step 46 or test strip inner surface 14 a (or both) to makethe capillary test space 48 more hydrophilic than the reservoir 30.

[0039] It may be desirable to have one of electrodes 32 completelywetted with fluid from reservoir 30 before the other of the electrodes30 is wetted. FIGS. 7-12 illustrate several alternative embodiments forachieving such sequential wetting. In the embodiments, elements incommon with those already described are numbered identically with theaddition of letter suffices (i.e., “a”, “b”, “c” and “d”). Such elementsare not separately described unless modified by the alternativeembodiment.

[0040] In FIGS. 7 and 8, it is desirable to completely wet electrode 32a before wetting electrode 39 a′. The electrodes 32 a, 32 a′ arepositioned side-by-side on test strip 14 a and equidistant fromreservoir 30 a. As shown in FIG. 8, the step 46 of the previouslydescribed embodiment is divided into two steps 46 a, 46 a′ opposingrespective ones of electrodes 32 a, 32 a′. A hydrophobic volume 50 a′ ispositioned between the steps 46 a, 46 a′. The volume 50 a′ functionssimilarly to side volumes 50 a (and 50 in the embodiment of FIG. 6) toact as a hydrophobic barrier to prevent fluid from flowing between thesteps 46 a, 46 a′. The steps 46 a, 46 a′ are spaced from test strip 14by spaces Sa and Sa′. Since space Sa is smaller than space Sa′, fluidfirst flows from reservoir 30 a into space Sa before flowing fromreservoir 30 a into space Sa′.

[0041] In the embodiment of FIG. 9, fluid is inclined to first flow ontostep 46 b before onto step 46 b′. However, in FIG. 9, the volume barrier50 a′ of FIG. 8 has been replaced with a ramp surface 47 b connectingsteps 46 b and 46 b′. Therefore, fluid can flow from space Sb to spaceSb′ after space Sb has first filled with fluid.

[0042] In the embodiment of FIGS. 10 and 11, the steps 46 c, 46 c′ arepositioned on opposite sides of the reservoir 30 c. If spaces Sc and Sc′are equal, fluid flows simulataneously into the spaces Sc and Sc′ butdoes not flow between the spaces Sc and Sc′. The spaces Sc and Sc′ maybe varied to change the rate of flow into the spaces Sc and Sc′.

[0043] The embodiment of FIG. 12 is similar to that of FIG. 9. Insteadof the ramp 47 b of FIG. 9 (which connects steps 46 b and 46 b′ directlyacross a side-to-side path), the ramp 47 d is U-shaped for fluid to flowfrom step 46 d to step 46 d′ in a U-shaped path A on a side of the steps46 d, 46 d′ opposite the reservoir 30 d.

[0044] From the foregoing detailed description, the present inventionhas been described in a preferred embodiment. Modifications andequivalents of such disclosure are intended to be included in theappended claims. For example, either or both of the reservoir 30 andcapillary test space 48 need not be an empty volume but could be filledwith an absorbent material.

The claimed invention is:
 1. An apparatus for collecting a body fluidfor testing for an analyte contained within said body fluid, saidapparatus comprising: a reservoir for receiving and collecting a flow ofbody fluid from a discharge end of a conduit; a capillary test spacepositioned to be in contact with said fluid in said reservoir after saidfluid has accumulated within said reservoir to a transfer volume offluid; and said capillary test space sized to wick said fluid from saidreservoir when said fluid in said reservoir attains said transfervolume.
 2. An apparatus according to claim 1 further comprising: testcomponents within said capillary test space for testing said fluid forsaid analyte.
 3. An apparatus according to claim 2 wherein: said testcomponents include electrodes for electro-chemically testing said fluid;said electrodes positioned within said capillary test space to be incontact with said fluid after said fluid is wicked into said capillarytest space.
 4. An apparatus according to claim 1 wherein: said reservoirincludes first and second spaced-apart ends; said discharge end of saidconduit disposed adjacent said first end; and said capillary test spaceis disposed adjacent said second end.
 5. An apparatus according to claim4 wherein a volume of said reservoir between said first and second endsof said reservoir is sized to be at least as great as said transfervolume.
 6. An apparatus according to claim 1 wherein said capillary testspace is vented.
 7. An apparatus according to claim 1 wherein materialdefining said capillary test space is more hydrophilic than materialdefining said reservoir.
 8. An apparatus according to claim 1 wherein:said conduit is a needle extending from a penetration end to saiddischarge end; said needle penetration end being exposed for penetrationinto a patient's skin to access body fluid for said fluid to flow alongsaid needle and discharged into said reservoir at said discharge end.